It is well established that the acquisition of pathogenicity islands (PAIs) assists the transformation of environmental bacteria to disease causing organisms. Yet, it remains poorly understood what limits or promotes the acquisition of PAIs among genetically similar strains. The O-antigen is a highly diverse and strain-specific structure covering the cell surface of Gram-negative bacteria that has been shown to play important roles in both pathogenesis and survival in the environment. I hypothesize that certain combinations of PAIs and O-antigens provide ecological fitness advantages in specific (micro) habitats (e.g., invertebrate guts, plankton, animal surfaces) and that this predisposes specific groups of strains to evolve towards pathogenicity. Vibrios are Gram-negative bacteria;certain strains infect marine animal and human hosts. Because Vibrios are abundant in marine habitats, these bacteria present ongoing threats to both humans and our national aquaculture. Thus, it is necessary to detect marine environments, which may be reservoirs for emerging pathogens in order to monitor these bacterial populations and predict potential pandemics. The Polz laboratory has isolated thousands of microdiverse Vibrios from defined marine habitats. This strain collection is the most exclusive of its kind and presents an excellent means to investigate the emergence of pathogenicity. My research will utilize this collection, as well as other Vibrios isolated from different marine habitats to: (i) characterize subpopulations of Vibrios based on core gene microdiversity using MLSA and phylogenetic approaches, (ii) determine the frequency that PAIs and virulence genes occur in these environmental Vibrios. Probes will be developed from known Vibrios virulence loci and other Ioci identified from published genomes using bioinformatics methods;these probes will be used to find virulence genetic elements using PCR and Southern blotting techniques, (iii) determine at what level O-antigen diversity co-exists with virulence loci and their correlates to specific environments. The wb* region encode genes that help assemble the O-antigen;this region will be isolated and sequenced to characterize this genetically diverse locus. The frequency and combination of both virulence loci and the wb* region will help determine if certain environments are breeding ground for pathogens. Pathogens infect particular hosts and cause disease. The relevance of this work is to determine if different marine environments are reservoirs for emerging pathogens that pose threat to both humans and commercial aquaculture. Results may lead to insights on how to monitor and predict bacterial outbreaks.